Not applicable
The present invention relates generally to the field of post chemical-mechanical polishing (post-CMP) cleaning operations, and more specifically to post-CMP cleaning solutions for microelectronic substrates.
The present day fabrication of semiconductor devices is a complex, multi-step process The chemical-mechanical planarization (CMP) process is now a well-established enabling technology used by most advanced semiconductor operation for planarization of various substrates for production of devices with design geometries of less than 0.35 micron.
The CMP processes involve holding and rotating a thin, flat substrate of the semiconductor material against a wetted polishing surface under controlled chemical, pressure and temperature conditions. A chemical slurry containing a polishing agent, such as alumina or silica, is used as the abrasive material. In addition, the chemical slurry contains selected chemicals, which etch various surfaces of the substrate during processing. The combination of mechanical and chemical removal of material during polishing results in superior planarization of the surface.
The CMP process, however, leaves contamination on the surfaces of the semiconductor substrate. This contamination is comprised of abrasive particles from the polishing slurry which may consist of alumina or silica with reactive chemicals added to the polishing slurry. In addition, the contaminant layer may comprise reaction products of the polishing slurry and the polished surfaces. It is necessary to remove the contamination prior to subsequent processing of the semiconductor substrate in order to avoid degradation in device reliability and to avoid the introduction of defects which reduce the manufacturing process yield. Thus, post-CMP cleaning solutions have been developed to cleanse the substrate surface of CMP residuum.
Alkaline solutions based on ammonium hydroxide have been traditionally used in post-CMP cleaning applications. To date, most CMP applications have been directed to aluminum, tungsten, tantalum, and oxide-containing surfaces.
However, copper is increasingly becoming a material of choice in the production of interconnects in semiconductor fabrication. Copper is replacing aluminum as the metal of choice in such fabrication. Conventional post-CMP processes are inadequate for cleaning surfaces containing copper. Copper, copper oxides, and the slurry particles are the contaminants that exist on the copper surface following this CMP process. The copper surface diffuses quickly in silicon and silicon dioxide. Therefore, it must be removed from all wafer surfaces to prevent device failure.
Post-CMP cleaning solution that is traditionally effective on alumina and silica-based CMP processes are not effective on copper-containing surfaces. Copper is easily damaged by these cleaning solutions. In addition, cleaning efficacy with the present post-CMP cleaning solutions has been proven unacceptable.
Nam, U.S. Pat. No. 5,863,344, discloses a cleaning solution for semiconductor devices containing tetramethyl ammonium hydroxide, acetic acid, and water. The solution preferably contains a volumetric ratio of acetic acid to tetramethyl ammonium hydroxide ranging from about 1 to about 50.
Ward, U.S. Pat. No. 5,597,420, discloses an aqueous stripping composition useful for cleaning organic and inorganic compounds from a substrate that will not corrode or dissolve metal circuitry in the substrate. The disclosed aqueous composition contains preferably 70 to 95 wt % monoethanolamine and a corrosion inhibitor at about 5 wt % such as catechol, pyrogallol or gallic acid.
Ward, U.S. Pat. No. 5,709,756, discloses a cleaning composition containing about 25 to 48 wt % hydroxylamine, 1 to 20 wt % ammonium fluoride, and water. The pH of the solution is greater that 8. The solution may further contain a corrosion inhibitor such as gallic acid, catechol, or pyrogallol.
Hardi et al., U.S. Pat. No. 5,466,389, discloses an aqueous alkaline cleaning solution for cleaning microelectronic substrates. The cleaning solution contains a metal ion-free alkaline component such as a quaternary ammonium hydroxide (up to 25 wt %), a nonionic surfactant (up to 5 wt %), and a pH-adjusting component, such as acetic acid, to control the pH within the range of 8 to 10.
Schwartzkopf et al., European Patent No. 0647884A1 discloses photoresist strippers containing reducing agents to reduce metal corrosion. This patent teaches the use of ascorbic acid, gallic acid pyrogallol among others for the control of metal corrosion in alkali containing components.
U.S. Pat. No. 5,143,648 to Satoh et al., which is herein incorporated by reference, discloses novel ascorbic acid derivatives as antioxidants.
Ward U.S. Pat. No. 5,563,119 discloses an aqueous stripping composition consisting of an alkanolamine, tetraalkylammonium hydroxide, and a corrosion inhibitor for cleaning organic residue from aluminized inorganic substrates.
There is a need for a post-CMP cleaning composition for copper-containing surfaces. Such a post-CMP cleaning composition must effectuate substantial particle removal from the target surface and prevent corrosion of the copper-containing substrate. Such a post-CMP cleaning composition must also refrain from attacking the process equipment used in the post-CMP process. Such a post-CMP cleaning composition should also be economical, work effectively through a wide temperature range. Such a post-CMP cleaning composition should also be useful in cleaning operations following CMP processes utilizing alumina or silica-based slurries.
The present invention is an aqueous cleaning solution for cleaning microelectronic substrates comprising a quaternary ammonium hydroxide selected from the group consisting of tetraalkylammonium hydroxide, wherein the alkyl contains one of C1 through C10 atoms or combination of C1 through C10 atoms; an organic amine selected from the group consisting of monoethanolamine, aminoethylethanolamine, N-methylaminoethanol, aminoethoxyethanol, diethanolamine, triethanolamine, C2-C5 alkanolamines, and combinations thereof; a corrosion inhibitor selected from the group consisting of ascorbic acid, L(+)-ascorbic acid, isoascorbic acid, ascorbic acid derivatives, citric acid, ethylenediamine, tetnaacetitic acid (EDTA), benzotriazole, and combinations thereof The alkalinity of the solution is greater than 0.073 milliequivalents base per gram of solution.
Thus in one aspect the present invention is a cleaning solution for cleaning microelectornic substrates, the cleaning solution comprising: 0.05 to 12.4 wt % quaternary ammonium hydroxide selected from the group consisting of tetraalkylammonium hydroxide, wherein the alkyl contains one of C1 through C10 atoms or combination of C1 through C10 atoms; 0.2 wt % to 27.8 wt % of a polar organic amine selected from the group consisting of monoethanolamine, aminoethylethanolamine, N-methylaminoethanol, aminoethoxyethanol, diethanolamine, triethanolamine, C2-C5 alkanolamines, and combinations thereof; an effective amount of a corrosion inhibitor selected from the group consisting of ascorbic acid (Vitamin C), L(+)-ascorbic acid, isoascorbic acid, ascorbic acid derivatives, benzotriazole, citric acid, ethylenediamine, tetraacetitic acid (EDTA), and combinations thereof balance water; and wherein the alkalinity of the solution is greater than 0.073 milliequivalents base per gram of solution.
In one aspect the present invention is a cleaning solution for cleaning microelectronic substrates comprising a) tetramethylammonium hydroxide, b) monoethanolamine, c) ascorbic acid, and deionized water. The alkalinity of the solution is greater than 0.073 milliequivalents base per gram of solution. Preferably, tetramethylammonium hydroxide is in the cleaning solution in an amount in the range from about 0.15 wt % to about 1.25 wt %, monoethanolamine is in the solution in an amount in the range from about 0.2 wt % to about 2.25 wt %, and ascorbic acid is in the solution in an amount in the range from about 0.10 wt % to about 0.9 wt %.
In still another aspect the present invention is a cleaning solution for microelectronic substrates, the cleaning solution consisting essentially of; from 1.5 wt % to 12.5 wt % of a concentrate consisting of 3.0 to 12.4 wt % quaternary ammonium hydroxide selected from the group consisting of tetraalkylammonium hydroxide wherein the alkyl contains one of C1 through C10 atoms or combination of C1 through C10 atoms, 5.0 wt % to 27.8 wt % of a polar organic amine selected from the group consisting of monoethanolamine, aminoethylethanolamine, N-methylaminoethanol, aminoethoxyethanol, diethanolamine, triethanolamine, C2-C5 alkanolamines, and mixture thereof; 2.0 wt % to 10.9 wt % corrosion inhibitor selected from the group consisting of ascorbic acid (Vitamin C), L(+)-ascorbic acid, isoascorbic acid, ascorbic acid derivatives, benzotriazole, citric acid, ethylenediamine, tetraacetitic acid (EDTA), and combinations thereof balance water; and, 87.5 wt % to 98.5 wt % deionized water, with the solution having an alkalinity greater than 0.073 milliequivalents base per gram of solution.
In yet another aspect the present invention is a concentrate composition for a cleaning solution for cleaning microelectronic substrates. The concentrate composition comprises from about 3.0 wt % to about 12.4 wt % tetramethylammonium hydroxide from about 5 wt % to about 27.8 wt % monoethanolamine, from about 2.0 wt % to about 10.4 wt % ascorbic acid, balance deionized water. A cleaning solution is made by either mixing from at least about 1.5 wt % to almost 100 wt % concentrate with deionized water. The concentrate can also be used without further mixing with water.